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Configurations

A configuration describes all parameters of a CRC algorithm. You either pick one of the predefined configurations, or define your own.

Predefined configurations

The library ships with a wide range of commonly used configurations, grouped by width in the enums Crc8, Crc16, Crc32 and Crc64:

CRC8 CRC16 CRC32 CRC64
CCITT XMODEM CRC32 CRC64
AUTOSAR GSM AUTOSAR
SAEJ1850 PROFIBUS BZIP2
SAEJ1850_ZERO MODBUS POSIX
BLUETOOTH IBM_3740
MAXIM_DOW KERMIT

Every member is a ready to use Configuration:

from crc import Calculator, Crc16

calculator = Calculator(Crc16.MODBUS)

Browse all configurations and their parameters

Custom configurations

To define a custom configuration you need to know the following parameters:

Parameter Description
width Width of the CRC in bits, e.g. 8, 16, 32, 64
polynomial Generator polynomial of the algorithm
init_value Value the register is initialized with
final_xor_value Value the final register is XOR'ed with
reverse_input Whether the input bytes are reflected
reverse_output Whether the final register is reflected 
from crc import Calculator, Configuration

config = Configuration(
    width=8,
    polynomial=0x07,
    init_value=0x00,
    final_xor_value=0x00,
    reverse_input=False,
    reverse_output=False,
)

calculator = Calculator(config)

Supported widths

This library currently only supports bit widths which are a multiple of a full byte: 8, 16, 24, 32, ...

Only know the name of the algorithm?

If you only know the name of a CRC algorithm and are unsure about its parameters, the CRC catalogue is a great place to look them up.

Next steps